The invention relates to a method for performing a pressure test on a tank and a tank filling apparatus for filling a tank with a gaseous pressurized medium, in particular in the form of hydrogen, using a filling apparatus for filling a tank with a gaseous pressurized medium, with: a tank feed line, comprising a first valve for shutting of the tank feed line, wherein the tank feed line is designed to be connected downstream of the first valve to a tank to be filled.
Vehicles which refuel with gaseous hydrogen as a fuel require specially designed filling apparatuses, which can convey the hydrogen under a comparatively high pressure (e.g. 700 bar) into the (vehicle) tank or another hydrogen tank. Such a filling station usually has a storage tank with liquid hydrogen or is directly connected to a hydrogen pipeline or other plant which can constitute a hydrogen storage tank. Since the hydrogen should be present in the gaseous phase for the filling, a filling station usually comprises a gas buffer storage tank, which is supplied from the aforementioned (liquid hydrogen) storage tank and holds available the gaseous hydrogen.
In order to ensure safety (explosion risk) for the surroundings when filling hydrogen tanks (e.g. vehicle tanks) with hydrogen and in order to create a standard for the filling process, a consortium comprising, amongst others, a number of car manufacturers agreed on standard SAE J2601. The standard provides, amongst other things, safety-related limits and performance requirements for the filling process. SAE J2601 makes provision such that hydrogen-powered vehicles are refueled within three minutes to 700 bar, without the temperature of the tank thereby rising above a temperature of 85° C.
Furthermore, standard SAE 2601 makes provision such that, prior to the filling of the tank, a pressure and tightness test is carried out; amongst other things, to ensure that the tank feed line of the filling station has been connected correctly to the tank to be filled.
The pressure in the tank is ascertained in said pressure test. This takes place by means of a short pressure surge from the filling station in order to open the tank concerned, which is secured by a tank valve (usually a non-return valve). The pressure established in the tank feed line, which is then equal to the pressure in the tank, is then measured in the filling station over a certain time (waiting period of approx. 5-20 s) in order to ensure that no significant drop in pressure occurs (tightness test), which would indicate a problem, such as for example a leakage in the tank feed line or in the connection to the tank.
The pressure surge for the pressure and tightness test is usually carried out directly from the gas buffer storage tank by the relatively rapid opening of valves, which leads to high mass flows from which enormous pressure peaks can then arise, so that downstream elements in the pipelines or the tank feed line, such as for example pressure transmitters, thermometers, flow measuring devices, valves and ramp regulators, are fully subjected to this pressure surge (approx. 800-850 bar). Furthermore, with this kind of pressure surge carried out directly from the gas buffer storage tank at the start (after said waiting period) of the actual filling process, there is often a further pressure peak in the downstream elements, which is due to a pressurized residual volume in parts of the pipeline. Such load alternations in the pipeline and the tank feed line contribute towards more rapid wear of the downstream elements and therefore to increased susceptibility to multifunction and shortening of the useful life of these components.
In addition, shut-off devices using temperature, pressure or drop in pressure (leakage) are usually no longer active at the time of the pressure surge, so that overheating, overfilling of a tank or partial filling of a non-tight tank can also occur in the worst cases during the pressure surge.
Proceeding from this, therefore, the problem underlying the present invention is to provide a method and a device of the type mentioned at the outset, wherein the aforementioned loads are reduced.
This problem is solved by a method for performing a pressure test on a (hydrogen) tank as described in detail below.